Solve for $n$ : $-11 = -15 + n$
Add $15$ to both sides: $ \begin{eqnarray} \\ \hphantom{-11 {+ 15}} &\hphantom{=}& \hphantom{n} \\ -11 &=& -15 + n \\ \\ {+15} && {+15} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -11 {+ 15} &=& n \\ \end{eqnarray} $ Simplify. $ n = 4$